Tuesday, August 17, 2010

"Here's a straightforward question. Imagine you are throwing a ball into a bin. Are you better off using an overarm or an underarm throw?

It turns out that this question has been surprisingly hard to get to grips with for physicists and biomechanicists alike. Today, however, Madhusudhan Venkadesany and Lakshminarayanan Mahadevan at Harvard University's Applied Math Lab, throw some additional light on the problem.

The difficulty is in the complexity of the problem. The arm, shoulder and wrist make up a many-jointed system that allows a large number of variations in throwing style. In addition, the parameters involved in throwing are difficult to compare. For example, a 5 per cent error in throwing angle does not easily stack up against a 5 per cent error in throwing speed because these quantities have different dimensions. It's like comparing apples and bananas.

Venkadesany and Mahadevan have a neat way round this conundrum. First, they consider only the simplest type of throwing model: an arm consisting of a lever pivoted at the "shoulder" which can throw either underarm or overarm. These throws can be described by two parameters: the angular velocity of the swing and the angle of the arm at release. Second, they introduce a natural length scale, called the arm length, and use this to make their analysis of launch angle and velocity dimensionless."